The study also found that the connection between the striatum and the prefrontal cortex – the part of the brain associated with behaviour and decision making – degraded with increased porn watching.

Nobody knows which came first, the small brain or the porn; although it is thought that porn causes the brain to shrink, it could be that people with smaller brains are more attracted to porn. Either way, this latest piece of research isn’t particularly flattering for porn bunnies.

And there are lots of them. According to aUniversity of East London survey, 97 per cent of boys and 80 per cent of girls between the ages of 16 and 20 have viewed pornography.In the United States, one in three women regularly indulge and 70 per cent of men between 18 and 24 visit pornographic websites at least once a month.

To make matters worse, brain shrinkage is but one in a list of the potential dangers of porn. The psychiatrist Norman Doidgehas reported that porn users may find it more difficult to become aroused by their real-life sexual partners; develop a “tolerance” to mainstream porn, causing them to turn to darker corners of the internet; and experience “potency problems”.

Moreover, it can cause men to try to recreate porn scenes in the bedroom, with embarrassing and often unpleasant results.

There can be little doubt that the pornographication of society is a worrying and potent trend, particularly for the young. The question is, what to do about it? Nobody wants to return to the world as it was before the sexual revolution, and putting the genie back in the bottle would require a level of authoritarianism that most people would find disturbing.

Ultimately, the answer must lie in moderation. If the dangers of excessive porn use are more widely known, perhaps enthusiasts will begin to regulate their use. That is, if their brains still function well enough to do so.